Boston Scientific - best known for making stents to prop open clogged heart arteries - has agreed to pay 840 pence per share, representing a premium of 36.6 percent to BTG's previous closing price, the companies said on Tuesday.

Shares of BTG soared by a third to 825p by 1200 GMT after touching 832p, their highest level since Jan. 2015. Up to Monday's close, they had slipped 19.3 percent this year, despite jumping last week on strong first-half results.

Boston Scientific said BTG's interventional medicine products, which use devices to deliver drugs to affected organs, would augment its capabilities in important areas of unmet need such as cancer and pulmonary embolism.

BTG, which has long produced drugs to treat overdoses and rattlesnake bites, has focused on interventional medicine in recent years, for example producing beads that target tumours.

Boston Scientific's Chairman and CEO Michael Mahoney said the addition of BTG's therapies would ultimately advance patient care in ways that could not be realised by either company alone, while also providing a strong return for investors.

BTG said it considered the terms of the offer to be fair and reasonable and it planned to recommend the deal to shareholders.

Australia's Sirtex, which also makes tumour-targeting beads, was eventually acquired by China-based CDH Investments in June, following an initial bid from Varian (VAR.N).

Boston Scientific said buying BTG was expected to boost adjusted earnings by 2 to 3 cents a share in 2019 and would be increasingly accretive thereafter.

The deal is Boston Scientific's biggest since its 2006 acquisition of heart device maker Guidant Corp for $27 billion, which left the company laden with debt and dealing with a slew of Guidant product recalls.

For BTG, the sale marks the end of the independence of an organisation that traces its roots back to Britain's National Research Development Corporation, founded by the government in 1948 to commercialise publicly funded research.

BTG was privatised in 1992 and listed on the London Stock Exchange three years later.